The present invention generally relates to outer-loop power control in wireless communication systems, and particularly relates to power control based on inferring a Frame Error Rate (FER) for a first channel of interest based on a signal received through an associated second channel.
Transmitter power control is an integral part of many wireless communication systems, including wireless communication networks based on Code Division Multiple Access (CDMA). Examples of CDMA-based network standards include, but are not limited to, IS-95, IS-2000 (cdma2000), and Wideband CDMA (WCDMA). In such systems, overall network capacity requires that transmitting mobile stations and network base stations constrain their transmit powers essentially to the minimum power levels necessary for reliable communication.
A typical approach to transmitter power control adopts both “inner-loop” and “outer-loop” power controls. In the inner-loop portion of such approaches, a first radio transceiver controls the transmit power of a second radio transceiver up or down such that it receives a signal of interest transmitted from the second radio transceiver at a target received signal quality. In turn, the slower, outer-loop portion of the power control scheme adjusts the inner-loop target up or down based on an observed quality metric, which is generally a frame error rate (FER) computed based on received data errors.
Transmit power control as described above relies on the presence of a suitable channel on which to base power control decisions. That is, conventional power control is based on either a fundamental channel carrying data traffic, or a dedicated control channel carrying control and other signaling information. In either instance, the channel of interest includes encoded data that may be decoded and evaluated for received data errors. It is this received data error evaluation that provides the basis for making intelligent decisions about whether to adjust the target received signal quality either up or down as part of the outer-loop power control mechanism.
In contrast to certain types of calls such as voice calls, packet data calls may be sent using discontinuous transmissions (DTX). That is, the traffic channel(s) used to carry packet data between a wireless network and a mobile station may be intermittently inactive. Without the presence of continuously received data frames on either a traffic channel or a dedicated control channel, the conventional approach to outer-loop power control becomes problematic as the basis for making adjustments to the target received signal quality is only intermittently available. One current approach to outer-loop power control during DTX is to gradually increase the inner-loop target during DTX periods, but this approach often results in greater than needed transmit power at the end of a DTX period, and particularly so at the end of longer DTX periods.